The present invention relates generally to optoelectronics, and more particularly, to variable optical attenuators.
Optical attenuators are employed within fiber optic data transmission systems to reduce optical signal power to within targeted ranges. Variable optical attenuators of several types have been used in the past. One such attenuator utilizes a rotatable disk in between a pair of optical fibers. The disk includes a number of partially opaque windows in different angular regions, each designed to attenuate optical energy by a different amount. Rotation of the disk thus produces step-wise changes in the attenuation characteristic. See, for example, U.S. Pat. No. 4,591,231 to Kaiser et al.
Variable attenuation has also been produced by varying the orientation between a pair of optical fibers. One of the fibers can be maintained in a fixed position while the other fiber is mounted on a movable surface that allows its terminal end to be axially or angularly moved relative to the fixed fiber. Differing attenuation values as a function of the moving fiber's position are thereby achieved due to the imperfect transmission between the fibers.
U.S. Pat. No. 4,904,044 to T. Tamulevich discloses a variable optical attenuator employing a flexible film with an optical density gradient that varies along its length. As the film is displaced across an optical coupling region between two fibers, the attenuation characteristic changes continuously rather than in a step-wise manner.
In recent years, advances have been made in the miniaturization of mechanical actuation devices and in the manufacturing of such miniature devices. In this light, it is desirable to produce a variable optical attenuator including a miniature actuator which is electronically or optically controlled to produce a desired attenuation by appropriately moving an attenuating member. This approach reduces the attenuator size as well as its electrical power consumption.